Studies Find Calcium Supplements May Increase Risk of Heart Attack

By Editor, on April 22nd, 2011

New studies, conducted by medical researchers at the University of Auckland, New Zealand, and the University of Aberdeen, Scotland, found that post-menopausal women taking calcium supplements (with or without Vitamin D) may be at increased risk of heart attack.

The WHI study had concluded that women who were given 1,000 milligrams of calcium and 400 international units (IU) of vitamin D per day as part of the study showed no significant risk of heart disease, compared to a control group who were randomly assigned to receive a placebo.

The New Zealand and Scottish researchers in the recent new study focused on the fact that some of the 36,282 women in the original WHI study reported that they were also taking personal calcium supplements, in addition to the supplements given to them in the study. Believing that this could have masked or distorted the initial findings, the researchers in this new study isolated and examined data from a subgroup of 16,718 women in the original WHI study who were not taking calcium supplements on their own when the WHI study began.

In their analysis, the researchers found that among the 16,718 women who were not taking calcium on their own, those who were assigned to take calcium (with or without vitamin D) as part of the trial were at modestly greater risk for heart attacks than those who were taking only the placebo in the trial.

“Calcium supplements with or without vitamin D modestly increase the risk of cardiovascular events, especially myocardial infarction [heart attack], a finding obscured in the WHI CaD Study by the widespread use of personal calcium supplements,” the researchers wrote.

However, the researchers found no statistically significant increase in risk of heart incidents among WHI study participants taking additional calcium supplements on their own in addition to the supplements assigned to them in the study, as compared to those taking only the supplements assigned to them in the study. “This suggests,” they concluded, “that there may not be a dose-response relationship between calcium supplements and the risk of cardiovascular events.” But, taking calcium (or calcium + vitamin D) supplements, as opposed to taking no calcium supplements, did correlate with a modestly increased risk of heart attack.

The Data Considered in light of 13 Other Studies:

“By itself, this analysis of the WHI CaD Study data does not provide definitive evidence of an adverse effect of calcium and vitamin D on cardiovascular events,” the researchers cautioned. “However, when these data are pooled with previously unpublished data from two other placebo controlled trials of calcium and vitamin D, there are consistent increases in the risk of myocardial infarction and stroke that are statistically significant and are of similar size to the risks observed with calcium supplements used without vitamin D,” they wrote.

Further, when these findings “are taken together with those from [other] trials of calcium used as monotherapy, they provide consistent evidence from 13 randomised, placebo controlled trials involving about 29 000 participants with about 1400 incident myocardial infarctions and strokes that calcium supplements with or without vitamin D increase the risk of cardiovascular events,” the researchers observed.

They further concluded that, “A reassessment of the role of calcium supplements in osteoporosis management is warranted.”

Additional Five-Year New Zealand Study:

In an introduction to their new study, the New Zealand and Scottish researchers also reported on the results of another recent study they had conducted. Called the “Auckland Calcium Study,” this study consisted of a “five year randomised, placebo controlled trial in healthy older women.” The researchers reported that data from their Auckland Calcium Study showed that “Calcium supplements significantly increased the risk of myocardial infarction [heart attack] by 31% in five trials involving 8151 participants where patient level data were available, and by 27% in 11 trials involving 11 921 participants where trial level data were available.”

Why may Calcium Increase Heart Attack Risk?

As to why calcium supplements may increase risk of heart attack, lead author Mark J. Bolland and his colleagues, wrote “Calcium supplements acutely increase serum calcium concentration by a modest amount, an effect that is sustained during long term treatment, as evidenced by lower levels of parathyroid hormone. Serum calcium concentrations are positively associated with carotid artery plaque thickness, aortic calcification, incidence of myocardial infarction, and mortality.”

The New Zealand and Scottish researchers conclude that the combined results of the studies referenced in their report, “justify a reassessment of the use of calcium supplements in older people.”

Calcium supplements are frequently prescribed for older women to combat osteoporosis. “That has long been standard medical advice,” according to recent articles in HealthDay and other publications.

What does this mean for you, if you are a post-menopausal woman at potential risk for osteoporosis?

Experts generally advise that women over 50 years old should get between 1,000 and 1,500 milligrams of calcium per day, preferably from natural sources in your diet. “With diet plus a supplement combined, women should be getting 1,000- to 1,500-milligrams a day,” said Dr. Susan V. Bukata, associate professor of orthopedic surgery at the University of Rochester Medical Center, as reported on HealthFinder.gov, a website of the U.S. Department of Health & Human Services. “Accumulating evidence has her urging patients to get their calcium from their diet, rather than reflexively telling them to take 1,200 milligrams of calcium a day,” reports the HealthFinder.gov article.

Nieca Goldberg, MD, medical director of the Women’s Heart Program at NYU Langone Medical Center in New York, told WebMD that “women must be aware of how much calcium they get through diet and how much they get through supplements to avoid getting too much of this mineral.” “Calculate how much you are eating through food and balance off the rest with supplements so it equals 1,200 milligrams of calcium a day for women older than 50,” she said.

Other experts caution that the determination of whether to take calcium supplements, and how much to take should be made with your doctor on an individualized basis. “Preventive health isn’t really a one-size-fits-all proposition,” Suzanne Steinbaum, MD, director of women and heart disease at Lenox Hill Hospital in New York, told WebMD. “If you are a woman who has a greater risk for heart disease vs. a greater risk of osteoporosis and fractures, perhaps calcium supplementation is not something for you to take,” she said.

Relatedly, Dr. Goldberg cautioned, “Women should also take a global approach to their heart disease risk and get risk factors evaluated,” she says. “Calcium intake alone is not the only risk marker for heart disease.”

Additional information on calcium and on Heart Disease in Women can be found on the linked pages of MedlinePlus, a website of the U.S. National Library of Medicine, National Institutes of Health. See also the Consumer Reports website, Health.org, on Calcium in Food.

For further information, see our resource pages on Heart Disease & Stroke, including:

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